What you actually want to do and what actually happens are two different things. You do not want to get involved in any fight. So you always try your best to avoid that.
But sometimes that might not be possible. You want to run away from that situation, but you cannot do that. The only option you have is to face it. What signal you are giving in a particular situation is very important.
The attackers will not show any mercy if they see you cannot do much to protect yourself. We expect to get help from other people. But the fact is, you will not find many people who risk their lives to save you.
Putting your head down with a view to protecting yourself will give the attacker more opportunities to attack you. You just cannot see what's going on when you put your head down. Of course, if there is gunfire, and you put your head down not to get shoot, that's a different situation.
If someone grabs your neck from behind, you can hit the attacker without turning around. You cannot escape from this if you do not do anything. The attacker will not let your move. Since he grabs your neck, he has more control.
To defend yourself, you can simply turn and face the attacker. Now you can strike him. Or, grab his hand that holds you and throw him on the ground. Then you can get out of there.